A new research found that the guidance of the magnetic field of a black hole has reversed in just four years, which gives a new perspective on the famous hair absence theorem.
Creating a black hole is easy. Just squeeze a lot of things in a small enough volume. No matter what you use. You can collapse stars, planets, old car tires, toil or missing left socks. The resulting black hole will depend only on the mass, rotation and electric charge of the original material.
At least that’s what we think. The idea that black holes have only three physical characteristics is called Hair absence theoremalthough it should be correctly called the hair absence hypothesis, as it was never formally proven. The good news is that we are now collecting direct observations of black holes SAG A* and M87*. Although these observations support the hair absence theorem, they also show us that things are a little more complicated.
According to the absence of hair theorem, a black hole cannot have a magnetic field. The magnetic field lines would constitute an additional structure or “hair”, and this is not possible because the field lines cannot pierce the black hole event horizon. But as a black hole has an intense gravitational field in the region near its event horizon, the dust and gas present in the region are compressed and overheat. As a result, there is a hot plasma torus around the black hole, which may have a strong magnetic field.
Although we cannot observe this magnetic field directly, we can study it by observing the polarization of radio light from the region. When light crosses the ionized gas, it becomes polarized. This polarization is aligned with the magnetic field lines; Therefore, observing the polarized light of M87*, we know the orientation of your magnetic fields.
The Supermassive Black Hole in M87 was first observed in 2017 and, with a mass of about 6 billion suns, it would not be to be expected to change quickly. This is generally true, but a new one analyzed observations from 2017, 2018 and 2021 and found that the polarization of the region is changing quickly. Over the course of just four years, the guidance of the magnetic field has reversed, as the earthly magnetic field changes every 200,000 years, but much faster.
The observed magnetic change is so drastic that we are not sure how it happens. One idea is that the regions charged within the Toro can protect currents from each otherallowing changes to happen quickly. Another is that strong turbulence within plasma flows causes drastic magnetic changes. There may also be an interaction between the rotation of the black hole and the rotation of the material stretch. But whatever the cause, it is evident that while black holes themselves do not have magnetic fields, they can lead to the creation of strong magnetic fields that change quickly near them. There is still a lot of black holes to teach us.
